1 use crate::consts::{constant, Constant};
2 use crate::rustc_target::abi::LayoutOf;
3 use crate::utils::{higher, is_copy, snippet_with_applicability, span_lint_and_sugg};
4 use if_chain::if_chain;
5 use rustc_errors::Applicability;
6 use rustc_hir::{BorrowKind, Expr, ExprKind};
7 use rustc_lint::{LateContext, LateLintPass};
8 use rustc_middle::ty::{self, Ty};
9 use rustc_session::{declare_tool_lint, impl_lint_pass};
10 use rustc_span::source_map::Span;
12 #[allow(clippy::module_name_repetitions)]
13 #[derive(Copy, Clone)]
14 pub struct UselessVec {
15 pub too_large_for_stack: u64,
18 declare_clippy_lint! {
19 /// **What it does:** Checks for usage of `&vec![..]` when using `&[..]` would
22 /// **Why is this bad?** This is less efficient.
24 /// **Known problems:** None.
28 /// # fn foo(my_vec: &[u8]) {}
41 impl_lint_pass!(UselessVec => [USELESS_VEC]);
43 impl<'tcx> LateLintPass<'tcx> for UselessVec {
44 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
45 // search for `&vec![_]` expressions where the adjusted type is `&[_]`
47 if let ty::Ref(_, ty, _) = cx.typeck_results().expr_ty_adjusted(expr).kind();
48 if let ty::Slice(..) = ty.kind();
49 if let ExprKind::AddrOf(BorrowKind::Ref, _, ref addressee) = expr.kind;
50 if let Some(vec_args) = higher::vec_macro(cx, addressee);
52 self.check_vec_macro(cx, &vec_args, expr.span);
56 // search for `for _ in vec![…]`
58 if let Some((_, arg, _)) = higher::for_loop(expr);
59 if let Some(vec_args) = higher::vec_macro(cx, arg);
60 if is_copy(cx, vec_type(cx.typeck_results().expr_ty_adjusted(arg)));
62 // report the error around the `vec!` not inside `<std macros>:`
70 self.check_vec_macro(cx, &vec_args, span);
77 fn check_vec_macro<'tcx>(self, cx: &LateContext<'tcx>, vec_args: &higher::VecArgs<'tcx>, span: Span) {
78 let mut applicability = Applicability::MachineApplicable;
79 let snippet = match *vec_args {
80 higher::VecArgs::Repeat(elem, len) => {
81 if let Some((Constant::Int(len_constant), _)) = constant(cx, cx.typeck_results(), len) {
82 #[allow(clippy::cast_possible_truncation)]
83 if len_constant as u64 * size_of(cx, elem) > self.too_large_for_stack {
89 snippet_with_applicability(cx, elem.span, "elem", &mut applicability),
90 snippet_with_applicability(cx, len.span, "len", &mut applicability)
96 higher::VecArgs::Vec(args) => {
97 if let Some(last) = args.iter().last() {
98 #[allow(clippy::cast_possible_truncation)]
99 if args.len() as u64 * size_of(cx, last) > self.too_large_for_stack {
102 let span = args[0].span.to(last.span);
104 format!("&[{}]", snippet_with_applicability(cx, span, "..", &mut applicability))
115 "useless use of `vec!`",
116 "you can use a slice directly",
123 fn size_of(cx: &LateContext<'_>, expr: &Expr<'_>) -> u64 {
124 let ty = cx.typeck_results().expr_ty_adjusted(expr);
125 cx.layout_of(ty).map_or(0, |l| l.size.bytes())
128 /// Returns the item type of the vector (i.e., the `T` in `Vec<T>`).
129 fn vec_type(ty: Ty<'_>) -> Ty<'_> {
130 if let ty::Adt(_, substs) = ty.kind() {
133 panic!("The type of `vec!` is a not a struct?");